Aside from Antarctica, South America was the last continent that modern humans colonised, says Claudio Latorre of the Pontifical Catholic University of Chile in Santiago. The first settlers arrived from North America at least 14,000 years ago, but their route south is a mystery. Most researchers assume they travelled through fertile corridors, perhaps down the west coast where seafood was plentiful, at least until you hit the desert.

"Extreme environments, such as the Atacama, were naturally assumed to be barriers," says Latorre. "This was not the case."

Atacama life

Latorre and colleagues excavated a site called Quebrada Maní, which lies 85 kilometres inland and only receives rain a few times a century.

Digging on a low hill surrounded by arid valleys, they found stone tools, animal bones, sea shells and the remains of a fireplace.

How did these people survive in the Atacama? Most of the desert's core was just as harsh then as it is today. But the team found the remains of plants at the site, suggesting that the valleys had seasonal marshes that acted as oases, and which have since dried up. Nowadays, only a few hardy microbes live there, often underground.

Oasis hopping

If people did enter South America along its west coast, Quebrada Maní could have been an important pit stop for heading inland, says team member Calogero Santoro of the University of Tarapacá in Arica, Chile. "Certain features of the site seem to correspond to a base camp," he says.

"We need to think in terms of oasis hopping," agrees Silvia Gonzalez of Liverpool John Moores University in the UK. She has found similar archaeological sites in Mexican deserts where there were once oases. "These barren sites were not barren then."

If the settlers really were journeying between widely separated oases, they must have been skilled navigators. Gonzalez thinks their society was probably already quite sophisticated. "Even at this early stage, there was probably trade," she says, with distant settlements exchanging items like sea shells and volcanic glass.

Few archeological sites in South America contain uncontroversial evidence for when the first peopling of the continent occurred. Largely ignored in this debate, extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability. Here, we report on a rare 12–13 ka human occupation from Quebrada Maní (site QM12), a plantless, near rainless landscape (1240 m asl and 85 km from the Pacific Ocean) located in the hyperarid core of the Atacama Desert. This location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central Andes during the latest Pleistocene. Excavations at QM12 yielded a diverse cultural assemblage of lithics, burned and cut bones, marine gastropods, pigments, plant fibers, and wooden artifacts alongside a prepared fireplace. Sixteen radiocarbon dates from site QM12 on charcoal, marine shells, animal dung, plant remains and wood reveal that the occupation took place between 12.8 and 11.7 ka. These results demonstrate that the Atacama Desert was not a barrier to early American settlement and dispersal, and provide new clues for understanding the cultural complexity and diversity of the peopling of South America during the Last Glacial–interglacial transition.

Fig. 2. Early archeological sites (with the oldest age of human occupation in calibrated 14C years BP) along the western Andean slope between 16° and 25°S. Dark dots: coastal sites, Green dots: sites located at elevations above 3000 m asl. Yellow area describes the extension of the Atacama Desert hyperarid core. Note that the QM site represents the first late Pleistocene (and oldest in northern Chile) site discovered within this extreme environment. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5. Photograph and detailed stratigraphy of an exposed section along the southeast wall at QM12c. Note the abundance of charcoal fragments and plant remains in layers 2–4. Red string marks the 0 cm reference. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 8. Plane view of the prepared fireplace (dotted red line- Feature 4; layers 3 and 4, quad N0W1). The concave enclosure is delimited by a salt concretion along with a rock placed in vertical position with signs of burning and ash adherence (arrow on the left), and also by a wooden pointed stick that has been burned on its tip (arrow on the right). Grid N1W1 shows the location of two protected pedestals, one containing bone fragments and charcoal, and the other (facing the wall) contains the vertical-oriented wooden artifact (with a prominent v-shaped longitudinal groove, see Fig. 7E). The other grids (N0E0 and N1E0, also indicated) show the base of levels 4 and 5, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)